The present invention relates to steering arms for steerable or radial railway trucks. More specifically, the side arms of each of the U-shaped steering arm sub-assemblies which comprise the steerable truck assembly, are provided with an undercut radius to improve the flexural strength between the side arm body portion and the side arm longitudinal segment without encumbering or interfering with the wheel position or operation. The undercut radius allows conventional foundry production and finishing practices.
Side trucks or steering arms for a vehicle truck are utilized to control railroad car trucks, especially against hunting or lateral movement during radial travel around curves. The objective of any of the radial trucks is adjustment of the axles, bolster and sideframe motion to accommodate radial movement around curves for relief of the lading from the shocks and jars incident to the contact between rails and wheel flanges.
Recent developments in steering arms for articulated railway trucks have concentrated on problems of lateral restraint and yaw flexibility between the two wheelsets of a truck in order to prevent high speed hunting. Changes in the steering arm structures for self-steering wheelsets are illustrated in U.S. Pat. No. 4,781,124 to List. However, one shortfall of that design is that the side arms of the steering arm structures project generally normal to the steering arm cross-beam, and are in close proximity to the wheel, thereby minimizing the available space for other truck components. As a consequence, the intersection between the steering arm assembly cross-beam and side arm is approximately a right angle. In operation, there is a repeated flexural load placed upon all joint intersections of these modern steering arm structures, and as noted, the clearances between the wheel and steering arm are minimal. The wheel, sideframe and bolster clearances, as well as the steering arm sizes, have combined to preclude or limit development of a stronger junctional relationship between the side arms and cross-beam, and of the side arms themselves. Although the addition of greater mass to a joint, or using a larger and smoother radius in a corner junction would act to increase the strength of the particular junction by dispersing the stresses over a greater area or mass, these alternatives are not readily available in many modern steering arm apparatus with the above-noted clearance constraints. A discussion of alternatives for increasing strength of intersecting arms or segments is provided in Stress Concentration Factors, by R. E. Peterson, John Wiley and Sons, 1974. It is noted that although circular fillets are utilized for ease of machining and drafting, they do not provide for minimum stress concentration. (See pages 80-83).
The development of stronger steering arm component junctions would allow tighter control of both the lateral restraint and yaw flexibility of the truck wheelsets and railcar, and provide greater control of high speed truck hunting. Working within the constraints of minimal clearances, a recent steering arm component junction was provided for in U.S. Pat. No. 5,224,428 to Wronkiewicz, assigned to American Steel Foundries, Inc. of Chicago, Ill. who is also co-owner of the present invention. In that steering arm assembly, the corner junctions of each side arm were provided with a compound fillet in the form of an elliptical radius. The compound fillet increased the flexural strength of each side arm over the circular radius, while simultaneously maintaining the necessary clearances between the steering arm and truck components.
However, producing a complicated compound fillet like the elliptical radius requires special quality assurances to maintain near-excellent steel quality so that surface or internal defects have no interplay with the formation of fatigue cracks. Using conventional foundry casting practices to maintain that level of consistent quality proves nearly impossible, and for this reason other methods for increasing the side arm fatigue life were explored. One successful method discovered was to increase the shot peening intensity during finishing, and this increase was achieved with the tumble blast method. However, this method precluded the use of grade B cast steels because they were found to be too soft for peening at the higher intensity. A second method investigated comprised tempering and quenching the casting, and although this method appeared favorable, the physical field distances between the tempering ovens and the quench tanks made this method to be unfeasible. Structural changes to the steering arm were also investigated, leading to the present invention.